Electrolytic condenser and paste composition therefor

ABSTRACT

A PLASTIC COMPOSITION CONSISTING OF ELECTROLYTE COMPOUNDS, BORIC ACID POLYESTERS OF ETHYLENE GLYCOL AND N-METHYL-2-PYRROLIDONE. WHEN USED AS AN ELECTROLYTE FOR AN ELECTROLYTIC CONDENSER, THE COMPOSITION FURNISHES SAID CONDENSER WITH GOOD ELECTRICAL PROPERTIES.

\ United States Patent [72] Inventors Yasukane Kihara 1 Tokyo;

Ushimatsu Moriyama, F ujisawa-shi; Yoichi Sets, Yokohama-shi, J span [54] ELECTROLYTIC CONDENSER AND PASTE COMPOSITION THEREFOR v 5 Claims, No' Drawings [51'] Int.Cl.... HOIg9/02 [50] FieldofSearch 252/62.2; 317/230. (Chemical AbstructsO [56] References Cited UNITED STATES PATENTS 3,302,071 1/1967 Stahr 252/62.2X 3,351,823 11/1967 Jenny..... 252/62.2X 3,487,270 12/1969 Alwitt 252/62.2X

FOREIGN PATENTS 1,480,996 5/1967 France Primary Examiner-James E. Poer Assistant Examiner-J. Cooper Artorney Kemon, Palmer and Estabrook ABSTRACT: A paste composition consisting of electrolyte compounds, boric acid polyesters of ethylene glycol and N- methyI-Z-pyrrolidone. When used as an electrolyte for an electrolytic condenser, the composition furnishes said condenser with good electrical properties.

ELECTROLYTIC CONDENSER AND PASTE COMPOSITION THEREFOR BACKGROUND OF THE INVENTION The present invention relates to a paste composition used as an electrolyte for an electrolytic condenser.

The typical known paste composition for an electrolytic condenser is a mixture of electrolyte compounds of borates and ethylene glycol. The borate of the mixture is added in amounts in excess of the upper limit of its solubility in ethylene glycol in order to furnish the condenser with good withstand voltage properties and great readiness for formation. However, such a composition has the drawbacks that it presents an unduly great viscosity at normal temperature due to the presence of a super-saturated borate, presents difficulties in being impregnated in a porous intermediate layer interposed ,between the electrodes of the condenser and fails properly to act as an electrolyte because of its tendency to solidify at low temperatures. Other disadvantages of the lrnown composition are, for example, that when used as an electrolyte in an electrolytic condenser, the composition 7 degrates the electrical properties and capacity stability of said composition when it is left unloaded.

SUMMARY OF THE INVENTION preciably low temperatures of 35 C. or lower, but is capable of forming a-good electrode. Further, an electrolytic condenser formed of the composition is extremely stable to temperature variations and displays no noticeable change in its capacity even whenit is left unloaded for long hours.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Electrolyte compounds available for preferable use in the pastecomposition of the present invention for an electrolytic condenser include one or more of boric acid, boric anhydride and borates such as ammonium tetraborate, ammonium pentaborate and barium hexaborate; phosphates such as potassium dihydrogen phosphate and zinc pyrophosphate; carbonates such as ammonium carbonate and magnesium bicarbonate; arsenates such as lithium dihydrogen arsenate and aluminurn arsenate; sulfates such as tributyl ammonium' sulfate and sodium hydrogen sulfate; acetates such as cadmium acetate and barium acetate; malonates such as lithium hydrogen malonate and diammonium malonate; aliphatic carboxylates such as magnesium acrylate, trimethylammonium maleate, ammonium tartrate and sodium cyanoacetate; aromatic carboxylates such as potassium benzoate, sodium hydrogen phthalate, and strontium salicylate; sulfonates such as magnesium ethane sulfonate, aluminum benzenesulfonate and sodium a-naphthalenesulfonate; phenolates such as sodium phenolate, dilithium resorcinate and zinc picramate; aliphatic amines such as ethylamine, ethylene diamine, digutylamine and triethanolamine; aromatic amines such as aniline, pyridine, indolate and melamine; and alkoxides such as sodiumethoxide, potassium isopropoxide, and zinc ter-bu toxide.

The boric acid polyesters of ethylene glycol used in the paste composition of the present invention may be prepared by subjecting boric acid or boric anhydride and ethylene glycol to dehydration and condensation reaction at a temperature of, for example, 90 to. I C and preferably in the presence of a catalyst. The nlol ecular weight of the polymer obtained is distributed between about 700 and about 750,000 in accordance with the propdrtions of the starting materials and reaction conditions involved. Where boric acid is used, it is preferably mixed with ethylene glycol in the molar ratio of about 1:] or about 2:1. The molar ratio of boric anhydride to ethylene glycol is about 1:1. Ratios widely departing from the aforementioned limits are likely to generate a polymer insoluble in N-methyl-Z-pyrrolidon, and such polymer is unavailable for use in the present inyention. The water which is produced with the progress of condensation reaction of boric acid or boric anhydride with ethylene glycol should be removed by heating the reaction product. The reason is that the presence of waterreduces the stability of the paste composition at temperatures of less than 0 C. If an organic solvent such as toluene is added to the reaction mixture, followed by heating, then the elimination 10f water will be more easily effected due to the azeotropy of :water with toluene.

The paste composition of the present invention consists of the boric acid polyesters of ethylene glycol and the abovelisted electrolyte compounds dissolved in N-methyl-Z-pyrrolidone. The N-methyl-2 -pyrrolidone itself has a favorable nature as the solvent component of an electrolyte and is capable of dissolving the electrolyte compounds and polyester polymers. This pyrrolidone the only material available at present for the purpose of the present invention. While there is no particular limitation on the proportions of the components of the paste compositioii of the present invention, experiments confirm that the following proportions are preferable.

Electrolyte compounds 01.5 to 30 parts by weight Boric acid polyesters of ethylene glycol 2 to 89.5 parts by weight 1 N-methyl-2-pyrrolidone 1 0 to 9.5 parts by weight The paste composition of the present invention is chemically stable and not easily affected by temperature variations. For instance, when left unloaded 1,000 hours at a temperature of 80 C. the composition did not display any change in its pH, viscosity and specific resistivity, resulting in no occurrence of precipitates. Further, experiments show that when left unloaded for long a conderiser using this composition as an electrolyte exhibits far less variations in the capacity and leakage current than the one prepared from the prior art composition. Such favorable properties of the paste composition of the present invention will naturally help to obtain an electrolytic condenser displaying better performance than has been possible with the conventiohal paste composition.

Further characteristics and concrete advantage of the present invention will be more fully appreciated from the i 1 specific examples which follow.

EXAMPLE 1 There were prepared in accordance with the recipe given in the table below 20 different polyester polymers of ethylene glycol.

Azeotropy with butanol Azeotropy with butauol Reaction conditions Average molecular weight of Boric Ethylene Tempera- Pressure, Water rereaction Polynwr No add, g. glycol, g. ture, C. mm. Hg moved, g. product 33. 1 66. 9 140 760 28. 8 2, 200 33. 1 66. 9 100 50 28. 8 2, 000 33. l 66. 9 93 760 28. 8 1, 800 33. 4 66. 6 180 760 29. 7, 500 33. 4 66. 6 140 760 26. 0 8, 400 33. 4 66. 6 100 50 29. 0 13, 000 33. 4 66. 6 93 760 29. 0 8, 000 50. 0 50. 0 180 760 29. 0 44, 000 50. 0 50. 0 140 760 29. 0 75, 000 50. 0 50. 0 100 50 29. 0 35, 000 50. 0 50. 0 93 7 29. 0 60, 000 54. 0 46. O 180 7 26. 6 1, 056 54. 0 46. 0 140 760 26. 6 1, 000 54. (J 46. 0 100 50 26. 6 1, 200 54. 0 46. 0 93 760 26. 6 1, 100

The polymersthus prepared were all soluble in N-methyl-2- pyrrolidone.

To some selected ones of these polymers were added electrolyte compounds and N-methyl-Z-pyrrolidone to prepare eight different samples of a paste composition of the present invention. Determination was made of the pH, static viscosity, stability at high and low temperatures and breakdown voltage of each sample. Determination of a breakdown voltage was made by immersing in 50 cc. of the sample three aluminum foils 99.99 percent pure, 100 microns thick and cm. in surface area which has been washedwith water, degreased and cleaned with alcohol, followed by drying and arranged at a 30 space of mm. in parallel relationship, and carrying out constant current formation at a current density of 50 ma./dm. with the central foil used as an anode and those on both sides thereof as a cathode.

There were further prepared eight different condensers from the aforesaid eight different samples. Determinationwas made with each condenser of the reduction of the static capacity, dielectric loss and variations in the static capacity and the equivalent series resistance after the condenser was left unloaded 1,000 hours at a temperature of 85 C. The conjected to constant current formation in an aqueous solution'of ammonium borate until 600 volts were reached, a cathode made of an aluminum foil 99.99 percent pure, mm. wide, 1,000 mm. long and 50 microns thick, and an intermediate layer interposed between both poles which comprised a sheet of high density kraft paper mm. wide, 1,100 mm. long and 45 microns thick and a sheet of medium density kraft paper 65 mm. wide, 1,100 mm. long and 20 microns thick. After being dried 1 hour at a temperature of 60 C. and a pressure .of 1 mm. Hg, the cylindrical body was immersed 4- hours in a sample paste composition at 60 C. at a pressure of 20 mm. Hg. The anode and cathode were fitted with a terminal and the cylindrical body was wound with kraft paper for insulation. Then the cylindrical body was. housed in an aluminum envelope which was closed at one end and had an insulation layer of pitch formed at said closed end. The open end of the envelope was encapped with a plate of insulating material in such a manner that the aforementioned anode and cathode terminals projected outside.

The recipe and properties of the respective paste compositions and the properties of the condensers prepared therefrom are presented in the table below.

. tion, percent Sample Polymer, Wt. percent 60 50 15 39. 5 4 15 0 (14) (17) 35 20 40 70 60 75 17 5 10 15 0.5 6 10 3 5.8 5.5 6.1 6.3 5.0 1 168 158 76 303 36 84 2 No change in pH, specific resistivity and viscosity and no occurrence of precipitates.) Low temperature stability, 35 C. hrs (No solidification and no occurrence of precipitates.) Brcakdown voltage, V. 595 610 680 630 650 Reduction of static capac y due t 15 18 22 13 24 9 15 19 Dielectric loss, 12 s., 25 C 0. 05 0.03 0.04 0.05 0.02 0.04 Variations in static capacity, perce 1.0 2.0 1.0 1.0 5.0 1.0 ancc,S2,-30 2.8 0.4 1.2 0.9

l Cadmium acetate. I 3 Barium hcxaborate. 3 Tctramcthylammonium dihydrogen phosphate. 4 Zinc pit-rate. 5 Potassium benzoatc. i Ammonium tartratc. T Trirnethylammonium maleatc. Ethylamine.

EXAMPLE 2 denser was prepared in the order of the following steps. There was formeda cylindrical body consisting of an anode made of an aluminum foil 99.99 percent pure, 50 mm. wide, 950 mm. long, 94 microns thick and having a static capacity of 8.2 micro F/dm. which, after etching treatment, had been sub- 75' There were prepared in accordance with the recipe given in the table below 12 different boric acid polyester polymers of ethylene glycol. These polymers were all soluble in N-methyl- 2-pyrrolidone.

- Breakdown voltage, V

Azeotropy with hutanol Average Home Reaction conditions molecular anhy- Ethylene Water weight of dnde, glycol, Tcmpera- Pressure, removed, reaction Polymer .\-o. 1:. tune. C. nun. llg 1. product 20. 3 70. T 180 T 15.7 750 20.3 if 1-10 760 15.7 710 N. 3 79. T 100 50 15. 7 800 20. 3 7t). 7 J3 760 15. 7 740 21. l 78. 1 180 760 16. S 220, 000 21. fl 78. 1 140 760 16. 9 750. 000 21. 7S. 1 10) 50 16. 9 355.000 21. f1 78. 1 83 760 16. 9, 601, 000 21. 78. 5 180 7 16. 5 2, 900 21. 5 78. 5 140 J 7 16. 5 2, 500 21. 5 7S. 5 100 50 16. 5 3,100 21. 5 78. 5 93 760 16. 5 2,700

To some selected ones of the polymers prepared were added electrolyte compounds and N-methyl-Z-pyrrolidbne to form seven different sample paste compositions. There were further fabricated seven difierent electrolytic condensers using each of said samples in the same manner as in Example 1'. Determination was made of the properties of the resultant cyanoacetate, potassium benzoate, sodium hydrogen phthalate, strontium salicylate, magnesium ethane sulfonate, aluminum benzene-sulfonate, sodium alpha-naphthalenesulfonate, sodium phenolate, dilithium resorcinate, zinc picramate, ethylamine, ethylene diamine digutylamine,

triethanolamine, aniline, pyridine, indolate, melamine, sodium condensers. The table below gives the recipe and properties of each paste composition and the properties of each electrolytic ethoxide, potassium isopropoxide and zinc butoxide.

3. A paste composit on according to claim 1 wherein the 25 condenser. boric acid polyesters of ethylene glycol are the condensation Sample 0 1o 11 12 ,13 A 14 15 Polymer, wt. percent, 67 55 A 2 35 85 No (21 (22) (2 (26) (27) N-methyl-2-pyrrolidone, Wt. percent. 30. 5 05 45 66 82 10 Electrolyte compounds, wt. percent. 1 2. 5 2 3 3 4 10 8 7 5 pH, 250 c 5. 3 6. 4 6.1 6.5 4. 9 Static viscosity, cps., J C 114 181 7 472 286 540 High tempeiature stability, 16 0.. 111%.

Low temperature stability, -35 C 120 hrs Reduction of static @5561 211135 12115151 65121 38 (No change in pH, specific resistivity and viscosity and no occurrence of precipitates.) (No solidification and no occurrence of precipitates.) 650 590 720 680 tion, percent... 16 7 Dielectric loss, 12 c./s., 25 C 0.03 0.05 Variations in static capacity, percent 85 C..

1,000 hrs 3.0 Equivalent seri resistance, S2, -35 1.8

1 Calcium isoprox'ide.

2 Pyridine.

. Diammonium malonate.

4 Lithium dihydrogen arsenate. 5 Aluminum benzene-sulionate. 5 Magnesium acrylate. 7 Ammonium carbonate.

We claim:

1. A paste composition for an electrolytic condenser consisting essentially of 0.5 to 30 weight percent electrolyte compound, 10 to 95 weight percent N-methyl-Z-pyrrolidone and 2 to 89.5 weight percent of boric acid polyesters of ethylene glycol having a molecular weight between about 700 and 750,000 and soluble in N- methyl-Z-pyrrolidone, said electrolyte compound being selected from the group consisting of boric acid, boric anhydride, salts of boric, phosphoric, pyrophosphoric, carbonic, arsenic, sulfuric, acetic, malonic, acrylic, maleic, tartaric, cyanoacetic, benzoic, phthalic, salicylic, alkyl sulfonic, and arylsulfonic acids, phenolates, aliphatic amines, aromatic amines and alkoxides.

2. A paste composition of claim 1 wherein said electrolyte compound is selected from the group consisting of boric acid, boric anhydride, ammonium tetraborate, ammonium pentaborate, barium hexaborate, potassium dihydrogen phosphate, zinc pyrophosphate, ammonium carbonate, magnesium bicarbonate, lithium dihydrogen arsenate, aluminum arsenate, tributyl ammonium sulfate, sodium hydrogen sulfate, cadmium acetate, barium acetate, lithium hydrogen malonate, diammonium malonate, magnesium acryla te,

trimethyl ammonium maleate, ammonium tartr'ate, sodium product of ethylene glycol and boric acid.

4. A paste composition according to claim 1 wherein the boric acid polyesters of ethylene glycol are the condensation product of ethylene glycol and boric anhydride;

5. An electrolytic condenser comprising a pair of aluminum foil electrodes, a porous layer interposed between said electrodes, a paste composition impregnated in said porous layer, an envelope housing said electrodes, porous layer and paste composition and terminals fitted to each of said electrodes to project outside said envelope, said paste composition consisting essentially of 0.5 to 30 weight percent electrolyte compound, 10 to 95 weight percent N-methyl-Z-pyrrolidone and 2 to 89.5 weight percent of boric acid polyesters of ethylene 

